Sharks and rays Flashcards
(18 cards)
What class do sharks and rays belong to?
Chondrichthyes
What are the two major groups within Chondrichthyes?
Batoidea (rays, skates, sawfish) and Selachii (sharks)
Elasmobranchs
What are the key physical features of batoids?
- Flattened body with enlarged pectoral fins fused to the head
- Gills on ventral side
- Spiracles on dorsal side
Name the four orders of batoids
- Rhinopristiformes (74 sp, guitarfishes, sawfishes)
- Myliobatiformes (236 sp, stingrays, eagle rays)
- Rajiformes (297 sp, skates)
- Torpediniformes (72 sp, electric rays)
Total ~679 species
Name the eight orders of Selachii
- Pristiophoriformes (8 sp, sawsharks)
- Hecanchiformes (6 sp, cow and frill sharks)
- Heterodontiformes (9 sp, bullhead sharks)
- Orectolobiformes (45 sp, carpet sharks)
- Lamniformes (16 sp, mackerel sharks)
- Carcharhinoformes (286 sp, requiem sharks)
- Squaliformes (135 sp, sleeper sharks, dogfish sharks)
- Squantiniformes (24 sp, angel sharks)
Total ~529 species
What is a heterocercal tail and who has it?
A tail with unequal lobes—upper longer than lower
True heterocercal tails are found in sharks
Why don’t sharks have swim bladders?
They rely on dynamic lift from body shape and static lift from liver lipids to maintain buoyancy
* Neutral buoyancy if submerged weight of fish is equal to hydrodynamic lift from pectoral fins and lift from caudal fin, negative buoyancy and sink if weight of fish is greater than hydrodynamic lift from pectoral fins and lift from caudal fin
If they stop swimming, they sink
What are the pros and cons of static lift in sharks?
Pro: Economical at low speed
Con: Lipids are bulky and not adjustable
Liver may exceed 20% body mass
What is the tail of the thresher shark used for?
As a whip to stun and catch prey
Morphological adaptation for hunting
What are the Ampullae of Lorenzini?
Electroreceptors in sharks’ heads that detect electrical signals, temperature changes, and salinity
Key for detecting prey at close range
How do sharks detect prey from afar?
Through a mix of vision, olfaction, lateral line sensing, and electroreception
Can detect prey km away
What is a major difference between shark and bony fish reproduction?
Sharks have few offspring with high parental investment; bony fish produce many eggs with no care
Sharks also use internal fertilisation
What are claspers and what are they used for?
Modified pelvic fins in male sharks used for internal fertilization
Involves direct copulation
Describe oviparity in sharks
Eggs laid externally with large yolk reserves in tough egg cases
Young hatched fully independent e.g skates, catsharks
What is ovoviviparity?
Embryos develop inside eggs retained in the mother’s body and may hatch before birth
No placental connection
What is uterine oophagy?
Embryos consume unfertilized eggs produced by the mother
e.g sandtiger sharks
What is true viviparity in sharks?
Embryo is nourished via placenta, like in mammals
e.g smoothhounds
How many sharks are estimated to be killed annually for fins?
Around 100 million
